Dr.Ali.A.Taqi
Fifth year students
2013-2014
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Gross Anatomy:
The cornea is the clear transparent anterior
one sixth of the fibrous tunic of the eyeball.
The cornea is set into the opaque sclera like
a watch glass, this corneo-scleral junction is
called the limbus.
The cornea has the following features:
1. It has a smooth brilliant surface.
2. It is very richly supplied with nerve fibers.
3. It has no blood vessels.
4. The cornea is the most powerful refractive
medium of the eye.
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Microscopic Anatomy:
1-Epithelium: This is a regular layer of uniform thickness of nonkeratinized stratified squamous epithelium.
2-Bowman’s Membrane: This is a clear uniform structureless
membrane that runs underneath the epithelium throughout the
cornea and ends abruptly at the limbus.
3-Substantia Propria: It forms about 90% of the entire thickness of
the cornea. It is made up of regularly arranged lamellae of
collagenous fibers associated with some elastic fibers lying in a
mucopolysaccharide matrix.
4-Descemet’s Membrane: This is a thin fine transparent and highly
elastic layer situated posterior to the substantia propria of the
cornea.
5-Endothelium: A single layer of flat hexagonal cells arranged
along the inner surface of Descemet's membrane.
Nerve Supply: Derived from the naso-ciliary branch of the
ophthalmic division of the trigeminal nerve through its long ciliary
nerves
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Functions of the cornea:
1. Optical: The cornea is the most powerful
refractive medium of the eye (42 Diopter).
2. Protective: The extreme sensitivity of the cornea
is an efficient protective mechanism producing a
very quick lid reflex.
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Inflammations of the cornea:
Inflammations of the cornea may be divided into two
types:
1-Ulcerative Keratitis: A corneal ulcer is a condition in
which there is destruction of some portion of both the
epithelium and the underlying Stroma of the cornea.
2-Non-ulcerative keratitis: is a condition in which the
Stroma of the cornea is only affected by the
inflammatory process while the overlying epithelium
remains intact.
Ulcerative keratitis:
Clinically it appears as a saucer-shaped yellowish
grey pit, which stains green with fluorescein
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Causes of Corneal Ulceration:
1-Exogenous Infections: The cornea is exposed
throughout life to miner trauma, virulent microorganisms present in the conjunctival sac may
gain access to the corneal tissue.
2-Endogenous Agents: The inflammation is
typically a cell-mediated immune response to a
foreign antigen and often occurs in the periphery
of the cornea, e.g. phlyctenular ulcer.
3-Chemical Agents: Acids, alkali, tincture of iodine
or lime produce corneal ulceration by destroying
the epithelium and the superficial layers of the
Stroma.
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4-Exposure: Incomplete covering of the
cornea leads to constant ulceration and
dryness of the cornea.
5-Loss of corneal sensation: Corneal
anesthesia, caused by trigeminal nerve
paralysis, leads to trophic changes in the
corneal epithelium resulting in degeneration
and ulceration. This condition is called
neuropralytic keratitis.
6-Vitamin A Deficiency: This leads to
degenerative changes in the corneal
epithelium leading to ulceration, it also
induces lack of resistance of the cornea to
micro-organisms of low virulence.
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Bacterial ulcerative keratitis:
Hypopyon ulcer: Also called pneumococcal ulcer, is a
disc-shaped ulcer of destructive nature near the
centre of the cornea associated with a diffuse
keratitis, a violent iridocyclitis and a hypopyon.
Aetiology:
Any defect in the basic defense mechanism of the
cornea, from trauma can predispose to corneal
ulceration. Hence, hypopyon ulcer often starts as a
minor abrasion to the cornea, e.g. by a scratch with
a finger nail or by a foreign body.
Virulent conjunctival pathogens can then lodge in the
exposed corneal Stroma and cause necrosis of the
corneal parenchyma.
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symptoms:
pain: it is of a neuralgic nature and is often referred to the eyebrow
region.
photophobia.
blepharospasm.
excessive reflex Lacrimation.
defective vision.
signs:
Circumcorneal vascular injection.
haziness and dullness of the corneal surface.
central disc-shaped ulcer.
Vascularization of the cornea.
mild to severe iridocyclitis.
secondary rise of ocular tension.
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Complications of the Hypopyon Ulcer:
Complication before Perforation:
1. Anterior uveitis.
2. Secondary glaucoma.
3. Corneal opacity.
Complication after perforation:
1. Prolapse of the iris.
2. Anterior Synechiae.
3. Leucoma Adherent.
4. Anterior Staphyloma.
5. Anterior Polar Cataract.
6. Corneal fistula.
7. Intra-ocular Hemorrhage.
8. Endophthalmitis and Panophthalmitis.
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Treatment of Uncomplicated Corneal
Ulcer:
1. Antibiotic to control infection.
2. Atropine to Relieve Uveal
Irritation.
3. Application of heat to increase
blood flow.
4. Wash out of conjunctival
discharge.
5. Protection of the eye.
6. Promotion of re - epithelialization.
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Viral Ulcerative Keratitis:
Herpes Simplex Keratitis:
Is primarily a superficial epithelial infection of the cornea,
usually develops after common colds or upper respiratory
tract infections, in association with herpetic vesicles in the
lips and face.
The disease has a definite tendency to recurrences. Primary
ocular involvement may present as an acute follicular
conjunctivitis or kerato-conjunctivitis with nonsupurative
preauricular Lymphadenopathy and often with notable
vesiculating periocular skin involvement.
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Clinical picture:
Symptoms:
Photophobia, reflex Lacrimation, pain blurring of vision,
foreign body sensation and corneal hypoesthesia.
Signs of Primary Ocular Infection:
Vesicles involving the lids and periorbital area.
Acute follicular conjunctivitis.
Fine or coarse epithelial punctate keratitis which may
progress to Dendritic figure.
Signs of Recurrent herpetic Keratitis:
Dendritic Epithelial Ulceration.
Geographical Herpetic Ulceration.
Stromal Herpetic Keratitis without or with Epithelium
Ulceration.
Herpetic iridocyclitis.
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Treatment of Herpes Simplex Keratitis:
Medical lines of Treatment:
Antiviral agents are usually the first line of treatment,
acyclovir eye ointment 5 times/day for up to 14 days.
The usual routine treatment of corneal ulcers, namely,
atropine drops, antibiotic against secondary bacterial
infection.
Surgical lines of treatment:
1. Debridement: removal of virus-containing cells is
indicated in recurrent Dendritic ulcers.
2. Lamellar Keratoplasty
3. Penetrating Keratoplasty.
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Herpes Zoster ophthalmicus:
1-Is caused by a virus identical with that causing
chicken-pox,
2-the chief focus of infection is in the Gasserian
ganglion whence the virus travels down one or more of
the branches of the ophthalmic division of the fifth
nerve.
3-Ocular complications usually arise when the nasociliary branch of the trigeminal nerve is involved.
4-The appearance of vesicles on the tip of the nose
often precedes corneal affection (Hutchinson’s rule).
Herpes Zoster affects elderly and often it is rare under
40 years of age.
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Keratitis in rheumatoid arthritis
PRESENTATIONS:
1-Peripheral corneal thinning.
2- Keratoconjunctivitis sicca.
2- Scleritis.
Rheumatoid arthritis is the most common collagen
vascular disorder to affect the peripheral cornea.
Peripheral corneal thinning (contact lens cornea)
is characterized by gradual resorption of peripheral
corneal tissue leaving the epithelium intact.
Because the central part of the cornea remains normal,
the appearance resembles a contact lens placed on the
eye .
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Treatment
1. Topical steroids may be useful in acute stromal
keratitis, but they should be avoided in peripheral
corneal guttering and keratolysis for fear of inducing
further corneal thinning and possibly perforation.
2. Systemic therapy with steroids and/or cytotoxic
drugs is required for active scleritis .
3. Conjunctival excision may halt the progression of
corneal furrowing in refractory cases.
4. Keratoplasty may be required either as an
emergency measure to prevent perforation or,
electively, to restore visual acuity.
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Keratoconus(conical cornea)
1-is a fairly common, progressive disorder
in which the cornea assumes an irregular
conical shape.
2-The hallmark of Keratoconus is central or
paracentral stromal thinning.
3-Both eyes are affected in about 85% of
cases, although the severity of involvement
may be markedly asymmetrical.
4-Keratoconus occurs with increased
frequency in the following disorders…….
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Systemic disorders include:
Down's syndrome
Turner's syndrome
Ehlers-Danlos syndrome
Marfan's syndrome
osteogenesis imperfecta
Ocular associations include:
vernal disease,
retinitis pigmentosa,
blue sclera,
aniridia and ectopia lentis.
The wearing of hard contact lenses and constant eye
rubbing have also been proposed as possible
predisposing factors.
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CLINICAL FEATURES
Onset is typically between the ages of 10 and 20 years, with
impaired vision in one eye caused by progressive
astigmatism and myopia.
Early signs, which are easy to miss, can be detected by the
following methods of examination:
1. Retinoscope shows an irregular 'scissor' reflex.
2. Keratometry initially shows irregular astigmatism where
the principal meridians are no longer 90 D apart and.
3. Photokeratoscopy or Placido's disc shows irregularity of
the reflected ring contours.
4. Slit lamp biomicroscopy shows very fine, deep, stromal,
oblique striae (Vogt's lines) which disappear with external
pressure on the globe.
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Late signs consist of the following:
1. Progressive central or paracentral corneal thinning, of as
much as one-third of the corneal thickness. This is associated
with poor visual acuity resulting from marked irregular
astigmatism with steep Keratometry (K) readings.
2. Bulging of the lower lid when the patient looks down
(Munson's sign;).
3. Epithelial iron deposits (Fleischer's ring) may surround the
base of the cone.
4. Central and paracentral corneal scarring in severe cases.
5. Acute hydrops results from ruptures in Descemet's
membrane and acute leakage of fluid into the corneal stroma
and epithelium Although the break usually heals within 6-10
weeks and the corneal oedema clears, a variable amount of
stromal scarring may develop.
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MANAGEMENT
1. Spectacle correction in very early cases can
correct regular astigmatism and very low amounts
of irregular astigmatism.
2. Contact lenses provide a regular refracting
surface over the cone.
3. Epikeratoplasty is an effective procedure in
patients intolerant to contact lenses without
significant central corneal scarring.
4. Penetrating Keratoplasty is indicated in
patients with advanced progressive disease,
especially with significant corneal scarring. The
visual results are excellent with a low risk of
allograft rejection.
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Contact lenses
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Contact lenses
Therapeutic indications for contact lens wear
The following are the main indications for contact lens
wear:
1.Irregular astigmatism associated with Keratoconus
can be corrected with a hard contact lens long after
spectacles have failed and long before corneal grafting
becomes necessary.
2. Superficial corneal irregularities: a contact lens can
replace a superficial irregular corneal surface by a
smoother and optically more perfect surface.
3. Persistent epithelial defects can be healed more
quickly by protecting the regenerating corneal epithelium
from the constant rubbing action of the lids,
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4. Recurrent corneal erosions, particularly if
associated with a corneal dystrophy, may require
long-term lens wear.
5. Descemetoceles can be covered with lens a
contact lens as a temporary measure to allow time
for natural healing to occur.
6. Protection of normal corneal epithelium in eyes
with trichiasis or threatened exposure Keratopathy
is another indication.
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Complications of contact lens wear
CONJUNCTIVAL COMPLICATION.
Giant papillary conjunctivitis (GPC)
is fairly common. Although any contact lens can cause the
condition, soft lenses are most frequently implicated.
Presentation :
may be months or years after beginning lens wear with
ocular itching after lens removal, increased mucus
production in the morning, photophobia and decreased
lens tolerance.
Blurred vision may also occur either from deposits on the
lens or when the lens is pulled towards the upper fornix by
the upper lid.
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CORNEAL COMPLICATIONS
The following are the main corneal complications of
contact lens wear:
1. Epithelial edema secondary to hypoxia which is
usually reversible.
2. Corneal Vascularization develops in some eyes
as a response to lens-induced hypoxia.
3. Sterile corneal infiltrates are usually small
peripheral opacities.
4. Microbial keratitis with bacteria, acanthamoebae
and fungi is the most serious, but fortunately a fairly
uncommon, complication.
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Treatment :
1. Lens hygiene should be optimized and the patient
may need to be re-instructed in the use of care
solutions.
2. Wearing time of the lenses should be minimized.
3. Attention should be paid to the fit of the lenses and
the material from which they are made.
4. Topical treatment with sodium cromoglycate is often
effective but long-term steroids should be avoided
because the hazards of steroid therapy may be greater
than the condition being treated.
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Corneal Degenerations and
Dystrophies:
Arcus Senilis:
It is an age-related hazy
grey line of fatty
degeneration which encircles
the cornea just inside the
limbus, no treatment is
necessary, however, its early
or excessive appearance
may indicate
hypercholesterolemia.
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Episcleritis
clinical features
Episcleritis is a common, benign, self-limiting and frequently
recurrent disorder which typically affects young adults. It is
seldom associated with a systemic disorder and never
progresses to a true scleritis.
The two clinical types of Episcleritis are simple and nodular.
Treatment
Simple Episcleritis usually resolves spontaneously within 1-2
weeks although the nodular type may take longer. Mild cases
may need no specific therapy but if discomfort is annoying,
topical steroids and/or topical non-steroidal anti-inflammatory
drugs (NSAIDs) may be helpful.
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Scleritis
Scleritis is a granulomatous inflammation of the sclera
coat of the eye. It is much less common than Episcleritis.
The condition covers a spectrum of ocular disease which
classification
The classification is based on the primary anatomical site
of the inflammation and the following associated changes
in the sclera vasculature.
Anterior scleritis
1. Non-necrotizing
•diffuse
•nodular
2. Necrotizing
•with inflammation
•without inflammation .
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Posterior scleritis
1. Non-necrotizing
•diffuse
•nodular
2. Necrotizing with inflammation.
associated systemic diseases
1. Rheumatoid arthritis
2. Connective tissue vascular disorders
3. Miscellaneous conditions include: relapsing
polychondritis, herpes zoster and surgically
induced scleritis.
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References
1.Lecture notes in ophthalmology, Bruce
James, Chris Chew, Anthony Bron,ninth
edition,blakwell.2003.
2.Clinical Anatomy and physiology of the
visual system, Lee Ann Remington, third
edition, Elsevier publications,2012.
3.Albert and Jakobiac’s,Principles and Practice
of ophthalmology, third edition, Saunders.
vol:1,Cornea chapter.
4. Parson’s diseases of the eye 2003.
5.Clinical ophthalmology Kanski J 2006.
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